Apparatus for testing traction coefficient and method of use thereof

ABSTRACT

An apparatus for testing fluids for coefficient of traction by measuring the thrust force at slip developed by a linear actuator due to traction between actuator drive shaft and rollers driven thereby. A continuous process for preparing a traction fluid by blending at least two components of different traction coefficients wherein the testing device is used to control the ratio of the two components to maintain the traction coefficient of the blend at a desired level.

' United States Patent Stenger Nov. 11, 1975 3.440.894 4/ l 969 Hammann 74/200 Primary Examiner-Alan Cohan [75] Inventor: Richard J. Stenger, Wilmington. Attorney, Agent. or FirmGeorge L. Church; Donald Del. R. Johnson; J. Edward Hess [73] Assignee: Sun Ventures, Inc., St. Davids. Pa.

[21] Appl. No; 511,396

An apparatus for testing fluids for coefficient of trac- Related Apphcauon Data tion by measuring the thrust force at slip developed by [62] Division of Ser. No. 320.357 v Jan. 2. I973, Pat. No. a linear actuator due to traction between actuator drive shaft and rollers driven thereby. A continuous process for preparing a traction fluid by blending at U-s. least two omponents of different traction oefficients CI.2 wherein the testing device is used to Control the ratio [58] Fleld of Search 137/3, 88; 74/200; of the two components to maintain the traction coeffi- 73/9' 10 cient of the blend at a desired level.

[56] References Cited 3 Claims, 3 Drawing Figures UNITED STATES PATENTS 2,992.65] 7/1961 Krofta 137/92 STORAGE STORAGE COMPONENT COMPONENT A B 20 22 I5 6 2| STORAGE I7 FINISHED TRACTION I9 6 FLUID ANALOG CONTROLLER ELECTRICAL ELECTRICAL I LEADS LEADS L I LINEAR ELECTRIC MOTOR AC'gUATOR 7 Y a la 1/ 9 L HYDRAULIC ll OR PNEUMATIC DISCARD SOURCE (OPTIONAL) US. Patent N0v.11,1975 Sheet2of3 3,918,468

Fig. 2

E m I J COEFFICIENT 0F TRACTION VALUES I000 f1./ min., 200 E 500,000 psi AS REPORTED BY DULING et 0|. IN US 3,608,385 SEPTEMBER 28, l97l.

** FOR IO PITCH, 250,000 psi 660 RPM SHAFT SPEED APPARATUS FOR TESTING TRACTION COEFFICIENT AND METHOD OF USE THEREOF This is a division of application Ser. No. 320,357 filed Jan. 2, 1973 now issued as US. Pat No. 3,839,897 on Oct 8, l974. L

BACKGROUND OF THE INVENTION Manufacturers of tractive power transmissions have long realized the need for lubricants having high dynamic coefficient of traction and which are non-corrosive and are sufficiently stable to retain those properties under severe stress to which such fluids are subjected during use. Concurrent with the needs for such fluids was a need to test tractive fluids under practical operating conditions.

A tractive device, which converts rotational movement into linear movement, in simplest form, could consist of two parallel cylindrical rollers, in tangential contact, one roller being the input member and the other the output member. The thrust force developed by such rotational contact is a direct function of contact pressure between the rollers, angular relationship between rolling elements and traction properties of fluid at rolling surfaces. he term coefficient of traction is preferred over coeffi ient of friction to connote rolling contact. Although tractive elements appear to be in contact, it is generally accepted that a fluid film is provided therebetween. Essentially all tractive drives require a fluid to remove heat and'to prevent wear at the contact surfaces. It is well established that the nature of this fluid has a profound effect on the performance of a threadlesstractive drive mechanism.

Coefficient of traction can be defined as the ratio of tangential force to normal load. The upper limiting value occurs at slip which is observed when rolling contact is on the verge of gross slip.

The present invention comprises a testing device for determining coefficient of traction under practical operating conditions by employing principles herein set forth and a process employing said device for preparing a tractive fluid of desired coefficient of traction from two or more fluids of different coefficientsof traction.

Previous'd'evices for testing coefficient of traction have not been completely satisfactory. Furthermore they have not been applicable to controlling the composition of a traction fluid composed of two or more fluids of different coefficients of traction.

l W. C. Hammann et al. describe three coefficient of v traction devices in Synthetic Fluids for High Capacity Traction Drives in American Society of Lubrication Engineers Preprint 69LC-l0.

A testing device referred to by Hammann et al. is described in US Pat No. 2,045,555, issued June 23, 1936,]. O. Almen, and consists essentially of a loaded thrust'bearing and a means for measuring torque. The device actually measures friction caused by the rolling of balls in their circular paths. This is not a true measurement of traction; one element is static, whereas in a traction drive two or more members are relatively rotatable.

' The aforementioned article also describes a two-disc machine which measures coefficient of'traction in terms of sliding velocity. Considerable computations and corrections must be applied to data from the twodisc machine to get values for coefficient of traction.

A research traction test machine isalso mentioned by I-Iammann et al. but not described in detail. The device 2 requires a two-gallon sample and several days of operating time.

None of the three aforementioned testing devices woule lend itself toa process application wherein the compoof a traction fluid is monitored and controlled continuously.

A linear actuator for converting rotational motion to linear displacement, also known as a mechanical transducer, provides a basis for'building thepresent testing device. Such linear actuators are commonly used on sliding doors, motion transfer devices, constant-force machine tool feeds, feeder-control equipment, etc. They employ a cylindrical shaft mounted for rotation about its longitudinal axis and a rider or roller block supported for linear movement along the axis of the shaft by a plurality of rollers mounted on the rider and engaging the outer surface of the shaft. The axes of rotation are disposed at an angle relative to the longitudinal axis of the drive shaft, and the surfaces of the rollers are urged into frictional engagement with the surface of the shaft so that, as the shaft turns, the rollers describe a helical path around'the shaft to move the rider linearly along the axis of the shaft. For a given shaft size and speed of rotation, the rate of travel of the rider along the shaft is determined by the angle which the roller axes make with the shaft axis. Also, the thrust which the roller block is capable of exerting is governed by this angle between the roller axes and shaft axis, and by the pressure exerted between the rollers and the shaft.

SUMMARY OF THE INVENTION As one embodiment, this invention provides an apparatus for testing traction fluids comprising:

a. a housing having means for conducting liquids thereto and therefrom;

b. a linear actuator for converting rotational to linear motion, said actuator including a smooth drive shaft and rotatable means within said housing abutting and tractionably drivable along the' shaft;

c. means for supporting and rotating said shaft;

d. andmeans for measuring thrust force along the longitudinal axis of the shaft due to tractionbetween the shaft and said rotatable means. 7

As another embodiment, this invention provides a continuous process for preparing a traction fluid comprising a blend of at least two fluids of different traction coefficients subject to variation from time to time, which comprises:

a. blending streams of said two fluids in a ratio adapted to produce a blend having a selected traction coefficient;

b. passing at least a portion of the blend through a testing device as specified in the aforementioned embodiment;

c. measuring the thrust force developed within the testing device;

d. and altering the ratio of said streams as changes in their traction coefficient levels occur to maintain a constant thrust by the test device.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, FIG. I is a schematic diagram of the testing device illustrating the relationship between linear actuator, supporting assembly, driving motor, fluid supply means and device to measure thrust force. FIG. 2 is a graphical illustration of the relationship between thrust force at slip and coefficient 3 of traction for selected fluids. FIG. 3 is a schematic illustration of a system for operating a continuous process for blending two components of different traction coefficients. wherein the testing device is used to control the ratio of two components to maintain the traction coefficient of the finished blend at a desired level.

DESCRIPTION OF THE INVENTION Referring to FIG. I, an assembly comprising a mounting I. an electric motor 2, a pair of bearings 3 and a smooth threadless drive shaft 4. support a linear actuator 5. The latter can be any suitable linear actuator such as those described by the following:

TABLE RELATIONSHIP BETWEEN 'IHRUST FORCE AND COEFFICIENT OF TRACTION Fluid Designation Coefficient Thrust Force.

Fluid in US. 3.608.385 of Traction* lbs at slip" Perhydro-ortho-terphenyl B .050 37 Perhydrogenated poly -mcthyl styrene 5 .049 37 Hydrogenated poly -meth \l styrene/polyhutene. 50/50 I .048 33 Hydrogenated polybutene 23 .044 30 ASTM oil No.3 (naphthenic) 35 .042 27 Hydrogenated polyoetene 46 .029 24 Hydrogenated ethylene-propylene copolymer oil 44 .026 22 \alues at I000 ft/min. 200F, 500.000 psi as reported by Duling ct al. in CS. Patent 3.603.385. September 23. l97l.

"For l0 pitch. 250.000 psi at rollers. (160 RPM vshaft speed.

Any other smooth shaft linear actuator can be employed. Sample fluid to be tested passes through conduit 6 and a flexible connector 7 to the linear actuator 5. Sample is withdrawn from the actuator through flexible connector 9 and conduit 8. Pitch of rollers within the actuator is fixed at a predetermined value of about l0. To develop a thrust force. pressure load on rolling elements within actuator is fixed at a predetermined value. as indicated by gauge 10, by means of an external hydraulic or pneumatic source I] acting through conduit 12 on diaphragm coverplate I3. The thrust force in pounds developed along the drive shaft axis due to traction between shaft and rolling elements contained within actuator is measured by instrument 14 which is attached between actuator 5 and mounting I by connector 15. In operation, a small continuous stream of fluid is introduced into line 6 while drive shaft 4 is in rotation. Thrust force is measured when slippage occurs between rollers and shaft within the actuator thus giving rise to a measure of traction coefficient.

In making measurement of thrust in the aforementioned test device, pitch on the rollers was set at pressure from external sources on 1 3/ 16-inch rollers was fixed at 90 psig for a ltd-inch shaft operating at 660 RPM. Mean compressive stress between shaft and rollers for tractive devices is generally in the range of 100,000 to 400,000 psi. The stress under the foregoing conditions wascalculated to be 250,000 psi according to the expression:

As another embodiment of this invention, the testing apparatus herein described is employed in a continuous process for monitoring and controlling the preparation of a tractive fluid from at least two components of different traction coefficients. Referring to FIG. 3 starting fluids having different coefficients of traction are supplied from containers l5 and 16. Fluids are withdrawn respectively through lines 17 and 18 by variable speed positive displacement pumps 19 and 20. Other suitable flow control devices are not excluded from the scope of this invention. Mixing occurs in line 21 while fluids are enroute to storage tank 22. A small sample stream is withdrawn through line 6 and monitored continuously in the test device according to this invention. The intensity of thrust force, at slip, is converted to an electrical signal by any conventional means. One such signal may be generated by a differential transformer. The signal, which is proportional to thrust force, is fed into a conventional analog controller, which amplifies the signal, compares said signal with one of a predetermined value and uses the differential signal to alter the speed of either pump 19 or 20 appropriately. The signal of predetermined value is proportional to the coefficientof traction for the finished product. Any deviation in generated signal from the predetermined value causes the necessary corrective changes in the ratio of the fluid components. Tested sample is passed from the testing device through line 8 and sent to storage tank 21 or discarded.

To avoid excessive wear of rolling elements within the linear actuator during long periods of testing, it may be desirable to change the mean compressive stress to same value less than 250,000 psi and vary the pitch to some angle other than 10. When used as a process con- 6 trol, provisions are made for rccalibrating the testing 2. A continuous process for preparing a traction fluid d i i di ll d replacing worn ll comprising a blend of at least two fluids of different Th invention l i traction coefficients sub ect to variation from time to time which comprises:

5 a. blending streams of said two fluids in a ratio adapted to produce a blend having a selected traction coefficient;

b. passing at least a portion of the blend through a thrust force measuring device comprising:

1. a variable pitch linear actuator in a housing havl. A continuous process for preparing a traction fluid comprising a blend of at least two fluids of different traction coefficients subject to variation from time to time which comprises:

a. blending streams of said two fluids in a ratio adapted to produce a blend having a selected trac- [0 tion Coefficient; ing means for conducting said liquid traction flub. passing at least a portion of the blend through a ids thereto and therefrom; said actuator having thrust force measuring device comprising: roller members mounted on a smooth rotatable l. A linear actuator in a housing having means for drive shaft; and having means for applying presconducting said liquid traction fluids thereto and Sure to the rolling members of Said actuator; therefrom, said actuator being mounted on and memls in h actuator for conducting Said l q tractionany movable along a Smooth rotatable traction fluids between the actuator and said roller members; and means attached to said housing adapted to measure the thrust force generated by axial movement of said actuator along said drive shaft; and.

c. and altering the ratio of said streams as changes in their traction coefficients occur to maintain a condrive shaft axially thereof, means in the actuator for conducting said fluids between said actuator and said drive shaft;

2. means attached to said housing adapted to measure the thrust force generated by movement of Said actuator along Said drive Shaft; stant thrust by the thrust force measuring device. c. and altering the ratio of said streams as changes in 3 A process according t l im 2 also including their traction coefficients occur to maintain a conmeans for recording said thrust force. stant thrust by the thrust force measuring device. 

1. A continuous process for preparing a traction fluid comprising a blend of at least two fluids of different traction coefficients subject to variation from time to time which comprises: a. blending streams of said two fluids in a ratio adapted to produce a blend having a selected traction coefficient; b. passing at least a portion of the blend through a thrust force measuring device comprising:
 1. A linear actuator in a housing having means for conducting said liquid traction fluids thereto and therefrom, said actuator being mounted on and tractionally movable along a smooth rotatable drive shaft axially thereof, means in the actuator for conducting said fluids between said actuator and said drive shaft;
 2. means attached to said housing adapted to measure the thrust force generated by movement of said actuator along said drive shaft; c. and altering the ratio of said streams as changes in their traction coefficients occur to maintain a constant thrust by the thrust force measuring device.
 2. means attached to said housing adapted to measure the thrust force generated by movement of said actuator along said drive shaft; c. and altering the ratio of said streams as changes in their traction coefficients occur to maintain a constant thrust by the thrust force measuring device.
 2. A continuous process for preparing a traction fluid comprising a blend of at least two fluids of different traction coefficients subject to variation from time to time which comprises: a. blending streams of said two fluids in a ratio adapted to produce a blend having a selected traction coefficient; b. passing at least a portion of the blend through a thrust force measuring device comprising:
 3. A process according to claim 2 also including means for recording said thrust force. 